PROGRESS TOWARD A STOCHASTIC ROCK MECHANICS MODEL OF ENGINEERED GEOTHERMAL SYSTEMS

Hot dry rock geothermal energy extraction experiments in artificial re servoirs created by hydraulic stimulation in naturally fractured cryst alline rocks have been undertaken in several countries over the last 2 0 years. The experiments have had mixed results in terms of fluid reco very, system impedance, and heat extraction. Numerical models have not yet delivered a generally agreed understanding of the processes and s ensitivities involved in reservoir creation and circulation. In this p aper a two-dimensional fracture network model is described, which atte mpts to address the problems of both reservoir creation and circulatio n using rock mass characterization and in situ stress data as the prim ary inputs with a view to encapsulating our present understanding of h ow such systems work. The model is a prototype for a three-dimensional version currently under development and is intended mainly for engine ering sensitivity studies. The basis of the model lies in approximatio ns of fracture mechanical behavior drawn from the rock mechanics liter ature, a very simplified analysis of the operative physical processes, and mapping of the connectivity of fracture networks to a fine resolu tion regular grid. Taken together, these permit the approximate resolu tion of what is normally a supercomputer problem on a personal compute r. The model is applied to field data gathered at Fenton Hill, New Mex ico; Hijiori, Yamagata Prefecture, Japan; and Rosemanowes, Cornwall, E ngland.